The method which is most commonly used for this purpose is a flotation method. A plurality of reference particles are sampled from a batch of particles to be characterised. This particle is cut, and pieces of each layer are separated in order to carry out the density measurements. These pieces are placed successively in a liquid whose density varies greatly in accordance with temperature. The temperature of the liquid is then varied and it is noted at what temperature the pieces drift to the bottom of the liquid. The density of the material constituting the piece corresponds to the density of the liquid at that temperature.
This method has the disadvantage of using toxic liquids. Furthermore, this characterisation method is slow and brings about the destruction of the particles of fuel characterised. Finally, its implementation is found to be extremely complex since the pieces of each layer must be separated and identified one by one.
In this context, the object of the invention is to provide a characterisation method which can be used for particles of nuclear fuel for a high-temperature reactor and which is non-destructive, environmentally-friendly and more rapid to implement.